MXPA01012525A

MXPA01012525A - Process and installation for recovery and purification of ethylene produced by pyrolysis of hydrocarbons, and gases obtained by this process.

Info

Publication number: MXPA01012525A
Application number: MXPA01012525A
Authority: MX
Inventors: Simon Yvon
Original assignee: Technip Coflexip
Priority date: 2000-12-07
Filing date: 2001-12-05
Publication date: 2005-09-08
Also published as: FR2817767B1; EP1215459B1; FR2817767A1; USRE40124E1; ATE289048T1; DE60108835D1; PT1215459E; DK1215459T3; EA200101185A1; CA2364354C; TR200403358T3; EA003348B1; CA2364354A1; ES2234792T3; EP1215459A3; US6578378B2; US20020198430A1; EP1215459A2; DE60108835T2

Abstract

Process for the high-yield recovery of ethylene and heavier hydrocarbons from the gas produced by pyrolysis of hydrocarbons (1) in which the liquid products (12-15, 23) resulting from the fractionated condensation of the cracking gas (1) for the recovery of almost all the ethylene, are supplied to a distillation column (C1), called the de-ethanizer, at different intermediate levels, at the top of which the vapor (31) of the column distillate is treated directly in an acetylene hydrogenation reactor (R1), the effluent containing virtually no acetylene being separated by a distillation column (C2) called the de-methanizer, into an ethylene- and ethane-enriched tail product (43), while the head product (44) is recycled by compression or treated for subsequent recovery of ethylene.

Description

PROCEDURES AND INSTALLATION FOR THE RECOVERY AND THE PURIFICATION OF ETHYLENE PRODUCED BY PYROLYSIS OF HYDROCARBONS, AND GASES OBTAINED BY THIS PROCEDURE FIELD OF THE INVENTION The present invention relates in a general manner and according to a first of its aspects, with the chemical industry and in particular with a high efficiency recovery method and ethylene purification, as well as other products coming from an gas produced by hydrocarbon pyrolysis. This invention also relates to an installation and the equipment intended to apply this method on an industrial scale.

BACKGROUND OF THE INVENTION A large number of works and patents dealing with the production, recovery and purification of olefins, show their industrial importance and the problems encountered in the course of the application of different procedures. Recently, the production capacity of ethylene units has reached and even surpassed the figure of one million tons per year, for a single line, which requires a new method for the conception of the procedure, equipment and control of unit. In recovery and purification systems, especially for ethylene, the removal of acetylene is a key element of purification. Due to their relative volatility with respect to ethylene and ethane, they can not be separated by distillation. In industrial practice, there are only two procedures applied: absorption of acetylene by a solvent and hydrogenation of ethylene and ethane. The first method brings into play a solvent which is usually the?,? - dimethylformamide (DMF) or the N-methylpyrrolidone (NMP), which allows acetylene to be preferably recovered in dissolved form. The second method, which corresponds to a catalytic hydrogenation, is generally carried out either by a treatment of all the gas emitted by the catalytic fractionation before the separation of the hydrogen contained therein, or already. either by a separate treatment of cuts containing the C2 hydrocarbons, after adding sufficiently pure hydrogen to transform all acetylene into ethylene and ethane. These two types of hydrogenation use palladium-based catalysts having different formulations.

The hydrogenation step of acetylene has also been the subject of numerous works and inventions that treat the catalyst system and catalyst formulations and expose the specific drawbacks linked to each of the hydrogenation technologies. Thus, in the case of the treatment of all the gas from the thermal fractionation emitted from the pyrolysis of hydrocarbons in a hydrogenation reactor, an acceleration reaction can be produced which corresponds to an acceleration of the kinetics of the conversion reaction of acetylene in ethylene (and also undesirable side reactions) due to a significant increase in the temperature of the catalyst together with the presence of a large excess of hydrogen (50 to 100 times the amount required by the stoichiometry). The ethylene can then be transformed into ethane and thus cause a sharp increase in temperature, which forces the reactor to depressurize immediately to avoid an explosion. In the case of the C2-only treatment, polymerization of the acetylene and progressive deactivation of the catalyst may occur, "due to the high concentration of unsaturated hydrocarbons in the cut to be treated, which requires a regeneration to a periodic replacement of the catalyst load Generally, a reserve reactor is installed in order not to interrupt production, and a stream of purified hydrogen must be used for the reaction, and these two aspects tend to increase investments for standby equipment or equipment that serves solely for the described purpose The present invention alleviates the respective drawbacks of prior known techniques, by purifying the ethylene-rich fraction at an intermediate stage of the process.

SUMMARY OF THE INVENTION Thus, the invention is related according to one of its aspects, with a fractionation process of a sensibly anhydrous gas emitted by the pyrolysis of hydrocarbons containing hydrogens and hydrocarbons, especially hydrocarbons from Ci to C3, including ethylene , propylene and acetylene, in at least one stream enriched with hydrogen and / or methane, at least one stream enriched with ethylene and depleted with acetylene, and at least one stream enriched with propylene, comprising the steps wherein: a) is cooled and the gas emitted from the pyrolysis of the hydrocarbons under pressure is progressively liquefied by the passage in a series of increasingly cold heat exchange zones, at least one condensate is separated from the pyrolysis gas after the step in each of them. the heat exchange zones, at least one of the condensates is enriched with propylene and at least one other condensate is enriched with ethylene and with ethane and concentrating the solution a smaller proportion of hydrogen, methane and acetylene, and collecting the residual gas, rich in hydrogen, b) evaporates at least in part, by decreasing the pressure, the condensate enriched with ethylene and ethane and the condensate enriched with propylene and heated, independently or not, 'in-' at least one of the heat exchange zones by thermal exchange with the fluids to be cooled, including at least the gas emitted from the pyrolysis , to provide respectively an at least partially evaporated fraction emitted from the expansion and heating of the fraction enriched with ethylene and methane, and an at least partially evaporated fraction emitted from the expansion and heating of the propylene enriched fraction, in a manner that at least part of the cold necessary for cooling and the progressive liquefaction of at least said gas emitted from pyrolysis is provided. s of hydrocarbons at the time of their passage in said successive zone of heat exchange, c) the at least partially evaporated fractions emitted from stage (b) are introduced into a part of a distillation column called deethanizer, the condensate at least partially evaporated enriched with ethylene and ethane is admitted at a point in the part of the distillation column called deethanizer higher than the at least partially evaporated condensate enriched in propylene, the part of the distillation column called deethanizer works under temperature conditions and pressure that allow to separate, in a higher part, a first gaseous dome stream enriched with ethylene and with ethane that concentrates, in smaller proportion, acetylene, hydrogen and methane, and in a lower part, a first stream of enriched liquid bottom in propylene, which is collected, d) the first current of the gaseous dome enriched with ethylene is sent and with ethane coming from step (c) in an acetylene removal zone by extraction with a solvent and / or by selective hydrogenation of acetylene by means of the hydrogen contained in the first stream of the dome, gas, to provide an essentially free of acetylene, and e) it is cooled and fractionated, in one. part of a distillation column called demethanizer, the gaseous stream essentially free of acetylene emitted from stage (d) in a second gaseous fraction of the dome, enriched with hydrogen and / or methane, which is collected, and a second liquid fraction of the bottom , enriched with ethylene and with ethane and essentially free of acetylene, which is also collected. The charge gas is generally essentially free of water in order to prevent ice deposits in the circuits at low temperature. Thus, a water content of less than 10 ppm by volume, preferably less than 1 ppm, is desirable. According to one of these aspects, the process according to the invention can apply the gas stream emitted from the pyrolysis of hydrocarbons at a pressure of 15.3-51 kg / cm2 (15-50 bar), preferably 28.56-38.76 kg / cm2 (28-38 bar), and the distillation zone called detanning can be at a pressure of 10.2-30.6 kg / cm2 (10-30 bar), preferably 14.28-24.48 kg / cm2 (14-24 bar), lower than the pyrolysis gas pressure.

According to one of these aspects, the process according to the invention can apply the evaporated condensates introduced in the part of the distillation column called deethanizer, which contain the dissolved hydrogen in a proportion such that the first stream of the gaseous dome concentrates the 2 to 10%, preferably from 4 to 5 mol%, of hydrogen, and step (d) can be applied by the selective hydrogenation essentially of the ethylene of the acetylene contained in the first stream of the gaseous dome, by means of the hydrogen contained in said first stream the gaseous dome of step (c), the temperature of the hydrogenation zone is comprised between 0 and 160 ° C included. According to one of its aspects, the process according to the invention can apply the hydrogen dissolved in the evaporated condensates introduced into the part of the distillation column called the deethanizer, so that it is the only hydrogen used for hydrogenation. carried out in step (d) In accordance with one of its aspects, the method according to the invention can be applied by sending in the upper part of the deethanizer d "stage (c) two or three condensates obtained after the successive passage of the gas of the pyrolysis respectively in two or three last heat exchange zones of step (a), considering that the first heat exchange zone is that which is the first to be in contact with the pyrolysis gas. The pyrolysis gas can be, for example, a naphtha pyrolysis gas or an ethane pyrolysis gas. According to one aspect of the method according to the invention, the second gaseous fraction of the emitted dome of the demethanizer can be purified by distillation for > recover ethylene and ethane. According to one of the aspects of the process according to the invention, the pyrolysis gas can be a pyrolysis gas of ethane or a mixture of ethane / propane and the second gas fraction of the dome emitted from the demethanizer can be mixed with the gas of pyrolysis without recovery of ethylene ', for a novel treatment in mixture with the pyrolysis gas of stage (a). According to one aspect of the method according to the invention, the hydrogen content of the first gaseous dome stream emitted from the deethanizer can be increased by the addition of hydrogen coming from the dome of a fluid separator, this The fluid comes from the cooling in a zone of heat exchange of the gaseous residual fluid, which comes from the cooling in the successive heat exchange zones of the pyrolysis gas. According to one of the aspects of the process according to the invention, a part of the second liquid fraction of the bottom, which comes from the demethanizer towards the deethanizer, is recycled, in order to reduce the acetylene concentration of the first current of the dome, gaseous, issued the deethanizer. According to one aspect of the process according to the invention, step (d) can be applied by extraction of acetylene by means of a solvent. According to one aspect of the method according to the invention, the concentration of carbon monoxide contained in the first dome stream, gaseous, can have a moderating effect on the rate of the catalyzed reaction in the acetylene elimination zone. . · According to another of its aspects, the present invention relates to a fractionation facility for a gas emitted from the pyrolysis of hydrocarbons that concentrates hydrogen and hydrocarbon L, especially hydrocarbons from Ci to C3, including ethylene, propylene and acetylene, in at least one stream enriched in hydrogen and / or methane, at least one stream enriched in ethylene and depleted with acetylene, and at least one stream enriched with propylene, comprising: a) means for gradually cooling and liquefying the Gas emitted from the pyrolysis of hydrocarbons under pressure, by passing through a series of increasingly cold heat exchange zones, and means for separating the pyrolysis gas into at least one condensate after passage in each of the heat exchange zones, at least one of the condensates is enriched with propylene and at least one other condensate is enriched with ethylene, and ethane, and concentrating in solution a smaller proportion of hydrogen, methane and acetylene, and means to collect the residual non-condensed gas rich in hydrogen. "'b) means for evaporating at least in part, by decreasing the pressure, the condenser enriched with ethylene and with ethane and the condensate enriched with propylene and means for heating independently in at least one of the heat exchange zones, by the thermal exchange with the fluids to be cooled, to provide respectively an at least partially evaporated fraction emitted by the expansion and heating of the enriched fraction of ethene and ethane, and an at least partially evaporated fraction emitted from the expansion and the heating of the fraction enriched with propylene, so that at least part of the cold necessary for cooling is provided and the progressive liquefaction of at least the gas emitted from the pyrolysis of hydrocarbons at the moment of its successive passage in the exchange zones of heat, c) means for introducing the at least partially evaporated fractions emitted from stage (b) in a In a distillation column called deethanizer, the at least partially evaporated condensate enriched with ethylene and ethane is admitted to a part of the distillation column higher than the at least partially evaporated condensate enriched with propylene, the part of the column of The distillation works under conditions of temperature and pressure that make it possible to separate, in an upper part, the first gaseous dome stream enriched with ethylene and ethane, which concentrates, in smaller proportion, acetylene, hydrogen and methane, and in a lower part, a first stream. of liquid bottom enriched with propylene that is collected, d) means to transport or send to the first gaseous dome stream enriched with ethylene and ethane that comes from stage (c), in an acetylene removal zone by extraction with a solvent and / or by the selective hydrogenation of acetylene by means of the hydrogen contained in the first gaseous dome current Bearing, to provide a substantially acetylene-free stream, and e) means for cooling and fractionating, in a part of a distillation column called demethanizer, the gaseous stream essentially free of acetylene emitted by step (d), in a second gas fraction of dome, enriched with hydrogen and / or methane, which is collected, and a second liquid fraction of the bottom, enriched with "ethylene and ethane essentially free of acetylene, which is also collected.

BRIEF DESCRIPTION OF THE FIGURES The invention is described with respect to the attached diagrams and showing two embodiments of the invention by way of illustration in a non-limiting manner. In the schemes: '^ Figure 1 shows the scheme of the principle of the treatment of a gas emitted from the pyrolysis of ethane / propane and / or liquefied petroleum gas (LPG); Figure 2 shows the same treatment applied to the gas emitted from the pyrolysis of naphtha and heavier hydrocarbons. For Figure 1, the number 1 designates the line of limitation of the pyrolysis gas sufficiently dry (for example less than 10 ppm of water) at a pressure chosen according to the required hydrogen pressure (for example from 15.3 to 51 kg / cm2 (15 a.50 bres), preferably between 28.56 and 38.76 kg / cm2 (28 and 38 bars)). The typical composition of a gas obtained by thermal fractionation of ethane is shown in the following table (in molar%): This gas is cooled in the heat exchanger 2 of multiple flows and in the interreamer 3 respectively, by the heat exchange with the cooled gases produced by the evaporation of the aforementioned condensates and by the evaporation of the propylene circulating in a gas circuit. classic cooling in closed circuit. The partially condensed gas feeds the separator 4 to a compressed temperature preferably between -30 and -40 ° C. The gas 5 collected in the dome of the separator 4 is further cooled, in the heat exchanger J 'of multiple flows 6, by the cooled gases produced by the evaporation of the condensates mentioned above, and more by the product 43, which is cut that comes from the bottom of demethanizer C2. The partially condensed gas in the exchanger 6 then feeds the separator 7 to a temperature preferably between -45 and -55 ° C. The gas 8 collected in the dome of the separator 7 is cooled in the heat exchangers 9 and 10, respectively by the cooled gases, as before and by the evaporation of the ethylene circulating in a closed circuit cooling cycle. The partially condensed gas feeds the separator 11 at a temperature preferably between -65 and -75 ° C. The liquid leaving the separator 11 is preferably divided into two parts, the product 12 and the product 13, previously decompressed respectively in the valves 12A and 13A. . : The product 12 is circulated countercurrently to the feed gas through the heat exchangers 9, 6 and 2 and feeds the upper section of the distillation column Cl. The product 12 is partially evaporated before feeding the column Cl called de-taining because of its role which is essentially that of separating ethane, ethylene and lighter hydrocarbons in the dome, and propylene and the heavier fractions in the bottom of the column. The liquid product 14 coming from the separator 7 is decompressed in the valve 14A and circulated countercurrently of the feed gas in the heat exchanger 6, mixed with the decompressed product 15 in the valve 15A emitted from the bottom of the separator 4, it is then circulated countercurrently of the pyrolysis gas in the heat exchanger 2. It is then evaporated by circulating it in the multi-flow exchanger 16. The product that heats the exchanger can be propylene coming from a closed-loop cycle or any another appropriate hot fluid. The product that leaves 17 contains essentially the hydrocarbons of C3 and the heavier hydrocarbons contained in the feed gas 1, with the exception of those contained in products 12 and 13 and which feed the Cl column at the level of its middle section. In a variant, the products 14 and 15 are separated separately from the Cl column. The distillation column Cl is provided with a reboiler heated by a hot fluid in a heat exchanger REB1, which is for example either process hot water or low pressure steam as a function of the temperature, preferably between 60 and 80 ° C, together with the bottom composition of the column. The operating pressure of column Cl is preferably between 14.23 and 24.48 kgf / cm2 (14 and 24 bar). •• i 'The product 18 stripped from the bottom of the Cl column can be treated in a conventional manner to recover the propylene in a unit not shown downstream of the process. The gaseous stream 19 coming from the separator 11 is further cooled in a heat exchanger 20 by the gas at low temperature as explained below, and in the heat exchanger 21 by the evaporation of the ethylene coming from a cycle of cooling in circuit closed. The partially condensed gas 22 is obtained at a temperature comprised between -90 and -100 ° C, feeds the ethylene separator 22 in a low part 22C. The liquid product 23 collected at the foot of the ethylene separator 22 is decompressed in the valve 23A, heated by the feed gas in the heat exchanger 20, it is optionally mixed with the product 13 that comes out of the separator 11 and that has been decompressed in the valve 13A, and it is again heated and partially evaporated in the heat exchangers 9 and 6. The resulting product 25 is the reflux of the Cl column. The method and the equipment described, which represent the first notable features of the invention, in which: The Cl column which is a deethanizer does not need a condensation system in the dome and the equipment to which it is linked. The product of the dome of the Cl column is a Cl cut that contains a certain amount of methane and hydrogen dissolved in the condensates that come from the separators 4, 7, 11 and 22. This quantity is scarcer than in the equivalent columns of the previously known methods and determines a supplementary cost advantage.

The pressure of the Cl column can be chosen in a range that allows to obtain a low background temperature and to avoid the known phenomena of fouling sensitive to temperature. 1 Returning now to separator 22, the gas 24, emitted from the dome of the lower part 22C of the separator 22, is further cooled in the heat exchanger 26 at a temperature generally lower than -120 ° C. The gas 24, cooled and partially condensed, is reintroduced as product 24C in the separator 22 in its upper part 22D, overheating the lower part 22C. The condensed fraction separated from the upper part 22D of the separator 22 is introduced into a channel 24A provided with a hydraulic screen, then inserted into the dome of the lower part 22C. The gaseous fraction 27 emitted from the head of the upper part 22D of the separator 22 is composed of a mixture of hydrogen, methane, carbon oxide and traces of ethylene The product 27 is heated in the heat exchangers 26 and 20 before being decompressed in the turbine 28. The product 30, which leaves the turbine 28, is heated by the feed gas in the complete series of exchangers 26, 20, 9, 6, 2 and 16 before being compressed in the machine 29, which is hooked to the turbine 28. The product 30A is discharged from the process.The distillate of the dome of the column Cl, the product 31, is heated in the heat exchanger 32 charge / effluent and in the heater 33 before enter the catalytic reactor Rl. The role of this reactor is to selectively hydrogenate the small amount of acetylene, generally less than 1 mol%, and to transform it into ethylene and ethane.This catalyst system is based on a known type, ^ for example based on palladium, and does not need a complementary description. The temperature is, for example, from 0 to 160 ° C. The second notable feature of the invention, compared with a known equivalent technique, is the fact that the hydrogenation is carried out on a gas mixture that already contains enough hydrogen and also three hydrocarbon compounds of the cut C2, ethylene, ethane and acetylene, to end the reaction in moderate and safe conditions. It is not necessary to add pure hydrogen. The typical composition of the product 31 is shown in the following table: H2 CO CH4 C2H, C2H¾ C2HZ c. + TOTAL % in mol 4.70 0. 04 4.86 57.10 32.40 0.80 0.10 100.00 The advantages with respect to the practice of the prior art are the following: A lower total volume flow rate, where a reduced catalyst volume, due to the presence of a low proportion of hydrogen only, for example from 4 to 5% in mol of hydrogen (more generally 2 to 10%), compared with 30-40% in traditional systems. A safer exploitation due to the decrease in the risk of the acceleration reaction in the case of an uncontrolled ethylene hydrogenation with an isothermal character. It is not necessary to use a complementary addition of purified hydrogen to feed the reactor. The catalyst poisons are removed in parts by condensation and fractionation of the C2 cut in the deethanizer. The low amount of carbon monoxide present in the mixture to be hydrogenated has a beneficial moderating effect on the behavior of the hydrogenation, since it allows to limit the frequency and speed of eventual acceleration reactions.

The reactor effluent Rl, which contains practically no more acetylene, is cooled in the heat exchanger 34, then passed through the charge / effluent heat exchanger 32, and the protection dryer 35 containing a dehydrating agent, for example a sieve. molecular (zeolite), or the like, to provide a dry gas 36. The product 36 containing the residual hydrogen and methane, and in addition to ethylene and ethane, is cooled in the reboiler REB2 of the C2 column and the subcooler 37 using the propylene that comes from a cycle of refrigeration in closed circuit. The partially condensed product 38 feeds the separator 39. The gas 40 collected in the dome of the separator 39 is further cooled in the heat exchangers' 6 and 41, respectively, with the cooled gases in the multi-flow exchanger 6 and with the ethylene vaporized that comes from a closed circuit refrigeration cycle in the re-cooler 41, and feeds the upper part of the column C2. The liquid 42 coming from the bottom of the separator 39 feeds the middle zone of the column C2. Column C2, called a demethanizer, operates at a pressure of 10.2 and 16.32 kgf cm2"" (10 to 16 bar), separates the lighter compounds than ethylene in the dome, and leaves the purified C2 hydrocarbons in the bottom product 43. The distillate 44 emitted from the dome 'of the column C2, is sent to the heat exchangers 9, 6, 2 and 16, to be heated and can finally be recycled towards the gas compression system outside the field of application of this invention . The bottom product 43 rich in ethylene is decompressed in the valve 43A, heated and partially vaporized in the exchanger 6 and can feed an ethylene purification column of the conventional type, not shown. According to this description, the preferred technology for removing acetylene is the hydrogenation carried out on the product 31, since acetylene is transformed into ethylene and ethane which are products that evaporate better. But, if one wishes to conserve acetylene, a solvent extraction system can be applied to the product 31, which will replace the entire circuit of the hydrogenation reactor with the equipment Rl, 32, 33, 34 and 35. This constitutes another comparative advantage with the procedures that use acetylene hydrogenation in all the thermal fractionation gas, which needs a modification to adapt a solvent extraction system.

For Figure 2, the number 1 designates the feed line of the thermal fractionation gas having a typical composition indicated hereinafter,% mol, such that it is produced by pyrolysis of naphtha or a similar charge.

The description is very similar to that of Figure 1, and it is therefore sufficient to define the data that are substantially different from the preceding ones. The gas number 1 cooled in the heat exchangers 2 and 3 feeds the separator 4 to a temperature generally comprised between less than 15 ° C and minus 30 ° C. The gas 5 is further cooled in the multi-flow exchanger 6 at a temperature comprised between minus 20 and minus 35 ° C. The gas flows through a limited number of countercurrent contact zones of the condensed liquid in the heat exchanger 54, which forms an integral part of the absorption column 7, and is cooled by the evaporated ethylene that comes from a cycle of cooling in circuit closed. A variant not indicated in Figure 2, but easily described by a person skilled in the art, consists of pumping a part of the liquid emitted from the separator 11, described later, towards the top of the absorption column 7, to generate in this column a countercurrent liquid product, which remains in the field of application of this invention. The gas 8, collected in the dome from the absorption column 7, contains only small amounts of C3 hydrocarbons, and heavier hydrocarbons, it is then cooled in the heat exchangers 9 and 20 before feeding the separator 11. The liquid product is divided into two parts: the product 12 is partially evaporated in the heat exchangers 9, 6 and 2, and then feeds the column Cl at an intermediate height, the product 13 is associated with the cold product coming from the exchanger 20 and is heated in the heat exchangers 9 'and 6 before feeding to the top of the column cl. The liquid product 14 coming from the absorption column 7 is likewise heated in the heat exchangers 6, 2 and 16 and feeds the column Cl in intermediate position. The distillation column Cl is reheated by a hot fluid circulating in a reboiler REB1, fluid that can be hot water from the process or from the steam at low pressure, or a combination of the two using also a secondary reboiler (not indicated, but familiar for the expert in the matter). The residue 18, collected at the bottom of the distillation column Cl, is treated to recover the ethylene and other valuable products, in the downstream units not shown. The gaseous product 19 coming from the separator 11 is cooled in the heat exchanger 20 by gas at low temperature and in the exchanger 21 by the evaporated ethylene that comes from a cycle of cooling in a closed circuit. The partially condensed gas 22B feeds the separator 22 to a temperature of -90 to -100QC. The liquid product 23 emitted from the separator 22, decompressed in the valve 23A is heated by the feed gas in the heat exchanger 20, is mixed with the product 13 coming from the separator 11 and is previously decompressed in the valve 13A. Returning now to the separator 22, the gas from the dome 24 is cooled in the exchanger 26 to a temperature generally comprised between -110 and -120 ° C to provide a fraction 24C which feeds the separator 22A. The upper part of the separator 22A receives the recycled liquid 50 after decompressing it in the valve 50A and which comes from the division in two flows of the pumped liquid of the separator 48. The separator 48 is fed by the distillate 46 of the methane rectifier 45. , previously cooled to a temperature generally comprised between -115 and -130 ° C in the heat exchanger 47. The fraction of the gaseous dome 52 emitted from the separator 48 is successively heated by the interchangers 47, 26, 20, 9, 6, 2 and 16, after the harvest. The fraction of the foot of liquid emitted from the separator 48 is pumped by a pump 49. A part of the fluid emitted from the pump 49 is sent in a conduit 51 comprising a valve, towards the top of the separator 45. The gas of the dome 27 , emitted from the separator 22A, is a mixture of hydrogen, methane, carbon oxide and traces of ethylene. This product is heated in the complete series of multiple flow heat exchangers described above and leaves the circuit in a crude hydrogen form. If necessary, the product 27 can be purified to obtain 95% hydrogen in a system of the Joule Thompson type before leaving the limit of this part of the process. In addition, a part of the product 27 can be mixed with the fraction 31 before the passage in the superheater 33, so that the concentration of hydrogen is increased, when necessary, in view of the hydrogenation of the acetylene in the reactor Rl. The liquid product 24A decompressed in the valve 24B is heated in the heat exchanger 26, then mixed with the product 23 coming from the separator 22 after it is decompressed in the valve 23A. The resulting product 53 is heated in the exchanger 20 by the feed gas, then mixed with the product 13 before being heated and partially evaporated in the heat exchangers 9 and 6. The resulting product 25 is the reflux for the Cl column. As described above, the Cl column constitutes the first notable feature of the invention. The description of the treatment of the product 31 from the distillation of the dome of the column Cl, is in all points similar to that given for Figure 1, and therefore it is not repeated here. It should be noted that this treatment constitutes the second notable feature of the invention. The typical composition of the product 31 is shown in the following table in mol%: The advantages over the past practice are similar to those that are described above. The product 36, which contains residual hydrogen, carbon monoxide and methane, and in addition to ethylene and ethane, is treated in a manner similar to the description in Figure 1, and is detailed in Figure 2. Because of the largest amount of methane present in the distillate of dome 44 of column C2, this product is treated in a methane rectification column 45, whose principle is known to the person skilled in the art. Thus, the gaseous product 44 emitted from the dome of the demethanization column C2 is introduced into the rectifier 45 after cooling and partial condensation in an exchanger "63, by evaporation of the ethylene coming from a cycle of cooling in a closed circuit. Liquid fraction collected at the foot of the rectifier 45 is cooled by the pump 55 to provide a liquid 56. The latter is separated in a first flow 58 which is cooled in the exchanger 26 to provide the flow 59, and in a second flow that is decompressed in a valve 57 to then be mixed with the fraction 40, after cooling in the heat exchangers 6 and 41. The treatment of the bottom product of the Cl column is similar to that given in the detailed description of Figure 1. The flow 59 is cooled in the heat exchanger 47, then it is separated into: a first fluid 60A, which passes a valve 60 to then be heated in exchanger 47 to provide a fluid 62, and /? a second fluid, which pass in a valve 61 which is then given with the fluid 60 after heating of the latter in the exchanger 47, to provide the fluid 62. The latter fluid 62 is then heated in the succession of heat exchangers 26 , 20, 9, 6, 2 and 16 and is, in this preferred embodiment, finally recycled to the gas compression system outside the scope of this invention. The removal of the acetylene from the product 31 can be carried out by absorption and extraction by a solvent in place of the hydrogenation without leaving the field of application of the present invention.

The present invention is illustrated and described following the preferred embodiments, but it should be understood that changes and modifications can be made by the person skilled in the art without departing from the scope of the present invention. It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates.

Claims

CLAIMS Having described the invention as above, the content of the following claims is claimed as property. 1. The fractionation process of a substantially anhydrous gas emitted from the hydrocarbon pyrolysis, which concentrates hydrogen and hydrocarbons, especially hydrocarbons from Ci to C3, including ethylene, propylene and acetylene, in at least one stream enriched in hydrogen and / or methane to at least one stream enriched in ethylene and depleted in acetylene and at least one stream enriched with propylene, characterized in that: a) said gas emitted from the pyrolysis of hydrocarbons under pressure is progressively cooled and liquefied by passing through a series of heat exchange zones, increasingly cold, is separated dichO '': pyrolysis gas in at least one condensate after the passage in each of the heat exchange zones, at least one of the condensates is enriched with propylene and at least one other condensate is enriched with ethylene and with ethane and the solution concentrates a smaller proportion of hydrogen, methane and acetyl The residual gas, rich in hydrogen, is collected, b) it is evaporated at least in part, by decreasing the pressure, the condensate enriched with ethylene and ethane and the condensate enriched with propylene and heated independently or not at all. at least one of said heat exchange zones, by heat exchange with the fluids to be cooled, including at least the gas emitted from the pyrolysis, to provide respectively an at least partially evaporated fraction emitted from the expansion and heating of the fraction enriched with ethylene and ethane, and an at least partially evaporated fraction emitted from the expansion and heating of the propylene-enriched fraction, so that at least part of the cold required for cooling and progressive liquefaction of the product is provided. at least said gas emitted from the pyrolysis of hydrocarbons at the time of its passage in said successive zone of heat exchange, c) was intro The at least partially evaporated fractions emitted from step (b) are discharged into a part of a distillation column called (Cl) deethanizer, the condensate. at least partially evaporated enriched in ethylene and in ethane is admitted at a point of said part of the column of "distillation (Cl) higher than the condensate at least partially evaporated enriched in propylene, said part of the column of distillation (Cl) it works under conditions of temperature and pressure that allow separating, in an upper part, a first gaseous dome stream enriched with ethylene and with ethane and concentrating, in smaller proportion, acetylene, hydrogen and methane, and in a lower part, a first liquid bottom stream enriched with propylene, which is collected, d) the first gaseous dome stream enriched with ethylene and with ethane is sent from step (c) in an acetylene removal zone (Rl) by extraction with a solvent and / or by selective hydrogenation of acetylene by means of the hydrogen contained in the first stream of the gaseous dome, to provide a substantially free stream of acetylene ethylene, and e) is cooled and fractionated, in a part of a distillation column called demethanizer (C2), the gaseous stream substantially free of acetylene emitted from step (d) in a second gaseous fraction of the dome, enriched with hydrogen and / or methane, which is collected, and a second liquid fraction from the bottom, enriched with ethylene and with ethane and essentially free of acetylene, which is also collected. 2. The process according to claim 1, characterized in that the gas stream emitted from the hydrocarbon pyrolysis is at a pressure of 15.3-51 kg / cm2 (15-50 bar), preferably 28.56-38.76 kg / cm2 (28-38 bar), and in which the distillation zone (Cl) is at a pressure of 10.2-30.6 kg / cm2 (10-30 bar), preferably 14.28-24.48 kg / cm2 (14-24 bar), lower than the pressure of the pyrolysis gas. The process according to claim 1 or claim 2, characterized in that the evaporated condensates introduced into the part of the distillation column (CÍ), called deethanizer, contain the hydrogen dissolved in a proportion such that the first dome current gaseous concentrates from 2 to 10%, preferably from 4 to 5% by mol, of hydrogen, and step (d) is applied by the selective hydrogenation, essentially in ethylene, of the acetylene contained in the first gaseous dome stream, by means of the hydrogen contained in the first stream the gaseous dome of step (c), the temperature of the hydrogenation zone is comprised between 0 and 160 ° C included. The process according to any one of claims 1 to 3, characterized in that the hydrogen dissolved in the evaporated condensates introduced in the part of the distillation column (Cl) called deethanizer, is the only hydrogen used for the hydrogenation carried out in stage (d). The method according to any one of claims 1 to 4, characterized in that two or three condensates obtained after the successive passage of the gas of the gas are sent in the upper part of the deethanizer (Cl) of stage (c). pyrolysis respectively in two or three heat exchange zones of stage (a), considering that the first heat exchange zone is the one that is the first to be in contact with the. pyrolysis gas. 6. The method according to any one of claims 1 to 5, characterized in that the second gaseous fraction of the dome / emitted from the demethanizer is purified by distillation to recover ethylene and ethane. from any one of claims 1 to 5, characterized in that the pyrolysis gas is a pyrolysis gas of ethane or a mixture of ethane / propane and in which the second gaseous fraction of the dome -demited from the demethanizer, is mixed with the gas of the pyrolysis, without recovery of ethylene, for a new treatment in mixture with the pyrolysis gas in step (a). 8. The process according to any one of claims 1 to 7, characterized in that the hydrogen content of the first gaseous dome stream, emitted from the deethanizer, is increased by the addition of hydrogen coming from the dome of a separator, of a fluid partially condensed, the fluid comes from the cooling in a zone of heat exchange of the gaseous residual fluid, which comes from the cooling in the successive heat exchange zones of the pyrolysis gas. The method according to any one of claims 1 to 8, characterized in that a part of the second liquid fraction of the bottom coming from the demetallizer is recycled to the deethanizer, so that the acetylene concentration of the first one is reduced. gaseous dome current, emitted from the deethanizer. 10. The process according to any one of claims 1 to 9, characterized in that in step (d) is applied by extraction of acetylene by means of a solvent. The method according to any one of the preceding claims, characterized in that the concentration of carbon monoxide contained in the first gaseous dome stream has a moderating effect on the rate of the reaction catalyzed in the acetylene elimination zone. (Rl) 12. Gases enriched with hydrogen and / or methane and / or higher hydrocarbons obtained by the process according to any one of the preceding claims. 13. The product enriched with ethylene obtained by the process according to any one of the preceding claims. 14. fractionation installation of a gas emitted from the pyrolysis of hydrocarbons that concentrates hydrogen and hydrocarbons, especially hydrocarbons from Ci to C3, including ethylene, propylene and acetylene, in at least one stream enriched in hydrogen and / or methane , at least one stream enriched in ethylene and depleted with acetylene, and at least one stream enriched with propylene, characterized in that it contains: a) means for progressively cooling and liquefying the gas emitted from the pyrolysis of hydrocarbons under pressure, by passing through a series of increasingly cold heat exchange zones, and means for separating the pyrolysis gas into at least one condensate after passage in each of the heat exchange zones, at least one of the condensates is enriched with propylene and at least one other condensate is enriched with ethylene, and ethanol and concentrating in solution a smaller proportion of hydrogen, methane and acetylene, and means to collect the residual non-condensed gas rich in hydrogen. b) means for evaporating at least in part, by decreasing the pressure, the condenser enriched with ethylene and with ethane and the condensate enriched with propylene and means for heating independently in at least one of the heat exchange zones, by exchange with the fluids to be cooled, to provide respectively an at least partially evaporated fraction emitted by the expansion and heating of the fraction enriched with ethylene and ethane, and an at least partially evaporated fraction emitted from the expansion and heating of the fraction enriched with propylene, so that at least part of the cold necessary for cooling and the progressive liquefaction of at least the gas emitted from the pyrolysis of hydrocarbons at the moment of its successive passage in the heat exchange zones is provided, c) means for introducing the at least partially evaporated fractions emitted from step (b) into a part of a distillation column called deethanizer, the at least partially evaporated condensate enriched with ethylene and ethane is admitted to a part of the distillation column higher than the at least partially evaporated condensate enriched with propylene, the part of the distillation column operates under conditions of temperature and pressure that make it possible to separate, in a higher part, a first gaseous dome stream enriched with ethylene and ethane that concentrates, in smaller proportion, acetylene, hydrogen and methane, and in a lower part, a first liquid bottom stream enriched with propylene that is collected, d) means for transporting or sending to the first gaseous dome stream enriched with ethylene and ethane that comes from stage (c), in an elimination zone of acetylene by extraction with a solvent and / or by the selective hydrogenation of acetylene by means of the hydrogen contained in the first gaseous dome stream, to provide an essentially acetylene-free stream, and e) means to cool and fractionate, in one part from a distillation column called demethanizer, the gaseous stream essentially free of acetylene emitted by step (d), in a second fraction. gaseous dome ion, enriched with hydrogen and / or methane, which is collected, and a second liquid bottom fraction, enriched with ethylene and ethane essentially free of acetylene, which is also collected.